This invention relates to an engine control and more particularly to an improved engine transient condition control for a direct injected, internal combustion engine.
In spite of the advantages of two cycle engines over four cycle engines in regard to complexity and high specific output, the environmental concerns are causing reappraisal of the continued use of two cycle engines. Specifically, the overlap between the scavenge port and exhaust port opening and closing gives rise to the possibility that unburned hydrocarbons may pass into the atmosphere through the exhaust port.
It has been thought that the performance of these engines can be improved by utilizing such methodologies as feedback control and/or direct cylinder fuel injection in order to improve their performance and make their continued use more feasible.
With feedback control systems, an engine combustion condition sensor such as an oxygen sensor is positioned in proximity to the combustion chamber or the exhaust system so as to sense the oxygen content of the exhaust gases at the completion of the burning cycle. By determining the amount of oxygen present, it is possible to tell if the engine is running rich or lean. Then, feedback control is possible to maintain the desired fuel/air ratio and, accordingly, improve the exhaust emission control.
Direct cylinder injection also is useful in improving engine performance. With direct cylinder injection, the amount of fuel injected per cycle can be more accurately controlled and this is particularly important with two cycle engines.
Of course, the use of direct cylinder injection and feedback control can be utilized with four-cycle engines as well as two-cycle engines. Although the utility may be somewhat more useful with two-cycle engines because of their inherent problems with exhaust emission control, many of the control strategies that are useful with two-cycle engines can also be utilized with four-cycle engines.
Feedback control generally, however, is most effective when the engine is running primarily in a steady state mode. Under this condition, the feedback control system can make adjustments in the fuel/air ratio so as to bring them to that appropriate for the specific running condition. However, with the normal types of injection control, control under transient conditions such as sudden acceleration are not particularly effective. Also with two cycle engines the increased amount of fuel required also raises the risk of the first injected fuel passing out of the exhaust port.
It is, therefore, a principal object of this invention to provide an improved transient control for the direct injection system of an internal combustion engine.
It is a further object of this invention to provide the improved transient control for incorporation in a feedback control system for a direct injected internal combustion engine.
One of the advantages of fuel injection and specifically direct injection is that the amount of fuel injected for a given cylinder and for each cycle can be accurately controlled. This permits the use of arrangements where the individual cylinders can be feedback controlled independently of each other. However, under transient conditions, the making of an immediate adjustment in the fuel/air ratio in a given cylinder can cause uneven running and can cause backfiring and other unsatisfactory conditions.
It is, therefore, a still further object of this invention to provide an improved transient control system for an internal combustion engine wherein the control during transient conditions is done with a specific cylinder other than the instantaneously operating cylinder in order to improve engine smoothness and avoid undesirable combustion conditions.